Full spine and full leg radiographic examinations, useful for assessment of scoliosis and for leg length, angulation, and deformity measurement and other diagnostic functions, require images that exceed the length of normal-sized radiographic films or other types of receiver media. In conventional practice, this extended- or long-length imaging (LLI) problem has been addressed using either of two basic approaches. The first approach uses an extra-long, non-standard sized imaging detector. This approach is straightforward and feasible when using x-ray film as the imaging medium, but becomes costly and impractical when using various types of digital radiography media. With Computed Radiography (CR) media, in which a photostimulable phosphor storage sheet or plate is exposed and digitally scanned in separate operations, the dimensions of the storage medium can be constrained by the dimensions of the CR cassette that houses the medium. There may be some flexibility for extending the size of the CR medium, as taught, for example, in U.S. Pat. No. 5,130,541 entitled “METHOD OF AND APPARATUS FOR RECORDING AND READING RADIATION IMAGE” to Kawai that shows the use of an elongated CR plate for long-length imaging. However, this approach may prove impractical and expensive, difficult to justify for most radiography installations.
For Digital Radiography (DR) detectors that directly transform received exposure energy to digital image data, the problem of extended-length imaging is much more complex and the fabrication and use of an oversized DR detector is seen as prohibitively costly and impractical. Instead, a second approach for extended-length imaging obtains portions of the full image on two or more standard-size detectors, adjusting the translational or angular position of the x-ray source between each image, then uses digital image processing to stitch the obtained sub-images together. This approach is taught, for example, in U.S. Pat. No. 5,111,045, entitled “APPARATUS FOR RECORDING AND READING RADIATION IMAGE INFORMATION” to Konno et al.; in U.S. Pat. No. 5,986,279, entitled “METHOD OF RECORDING AND READING A RADIATION IMAGE OF AN ELONGATE BODY” to Dewaele; and EP 0 919856A1, entitled “METHOD AND ASSEMBLY FOR RECORDING A RADIATION IMAGE OF AN ELONGATE BODY” to Dewaele et al. A variation on this approach also sequentially re-positions a single DR detector along the anatomy to be imaged so that the same detector is used to obtain images at two or more positions.
Among the factors that make long-length imaging using a single DR detector more complex is the image transfer and refresh timing of the DR detector hardware. Even with higher speed circuitry and advanced techniques for image storage and transfer, the time interval required between image captures can be on the order of a few seconds. Inadvertent movement of the patient between images can present difficulties for reconstruction of the full length image from individual component images. The timing of DR exposure and detector and radiation source movement or adjustment between images provides significant complications for the designer of DR systems.
Solutions that have been proposed thus far generally require complex interaction and coordination between components that are shifted between positions for obtaining individual images. Translation of the imaging detector relative to the patient has been proposed using various techniques. For example, U.S. Pat. Nos. 4,613,983 entitled “METHOD FOR PROCESSING X-RAY IMAGES” to Yedid et al. and 5,123,056 entitled “WHOLE-LEG X-RAY IMAGE PROCESSING AND DISPLAY TECHNIQUES” to Wilson disclose X-ray systems for imaging a human subject lying on a table. Either the table or both the X-ray source and table are then moved to produce, in quick succession, a series of overlapping electronic images which are then combined into an elongated image for display or printing. Similarly, Warp et al. in U.S. Pat. No. 7,177,455 entitled “IMAGE PASTING SYSTEM USING A DIGITAL DETECTOR” describes shifting the position of a DR detector and adjusting the corresponding position of the x-ray source for obtaining individual images that can be stitched together using digital techniques.
Commonly assigned U.S. Pat. No. 6,807,250 entitled “COLLIMATION DEVICE AND METHOD FOR ACQUIRING A RADIATION IMAGE OF A LONG BODY PART USING DIRECT DIGITAL X-RAY DETECTORS” to Wang et al. describes the use of a shutter or other opaque element having an opening that is used in conjunction with the x-ray detector and that can be variably positioned relative to a movable DR detector in order to obtain each separate image for a long-length imaging exam. However, while this solution addresses the need for adjustment of the x-ray source, a mechanism is employed for synchronizing the position of the shutter relative to the detector, which typically requires a controller that also tracks DR detector position.
Although techniques disclosed thus far may be workable for obtaining separate images of the patient that can then be stitched together, a number of practical problems remain. In particular, the proposed solutions noted earlier each require relatively complex and costly systems. For example, multiple control processors are typically used to provide and to coordinate relative movement between the patient, exposure device, and detector. Because of this, these solutions would not be readily adaptable for use as retrofit apparatus for existing x-ray systems, but would need installation of new exposure, sensing, and control and monitoring equipment.
Thus, it can be appreciated that there is a need for a long-length imaging solution that is relatively low cost and that allows x-ray exposure energy to be directed to a digital radiography detector that may be variably positioned at any of a sequence of positions along a linear path in order to obtain a portion of the longer image at each position. A solution that meets these requirements without requiring complex communication between detector-positioning and beam-positioning subsystems would be particularly advantageous.